Type of Iris

I have an iris plant I am trying to identify. I think it is a Pacific Coast iris, but I'm not sure. The rhizome is 1 1/2" long and the width of a small baby finger. It was given to me by a friend about 5 years ago. She said the flower is purple, although I haven't had it bloom. I had it in a pot and was quite surprised that it had very dark earth (I'm thinking it's acidic). It clumps together in its growth habit and is evergreen. The leaves are 1/4" wide by 22" long. They are reed like and curl downward when they dry out.